Dohrwardt 2

CHME 498

Undergraduate Research

Final Report

New Mexico State University

Miscibility Between Poly (Ethylene Oxide) and Various Acrylate Polymers

Research Performed by Chelsea Dohrwardt

December 12th, 2016

ABSTRACT

The purpose of blending polymers is to generate a unique polymer with the ideal mechanical properties for application. For instance, in lithium-ion batteries it would be ideal to create a polymer that has the mechanical strength of a solid with ionic conductivity of a liquid. However, blending polymers is not as simple as mixing the two together. The purpose of the research performed this semester was to identify if poly (ethylene oxide) and various poly acrylates are miscible. Due to error and inexperience, the results obtained were inadequate. Future endeavors should re-examine this experimental procedure with the addition of ionic liquids.

TABLE OF CONTENTS

1. INTRODUCTION.4

2. LITERATURE REVIEW......5

i. Phase Diagrams and Behavior....5

ii. Flory-Huggins Regular Solution Model.6

iii. Instrumentation for Analysis..7

3. EXPERIMENT.9

i. Solution Casting9

ii. Analysis10

4. PROGRESS AND FUTURE PLANS.11

i. Progress....11

ii. Results..12

iii. Future Plans.15

5. CONCLUSIONS.15

6. REFERENCES........16

1. INTRODUCTION

The blending of polymers has been the highlight of various research experiments because of its vast application. The challenge of blending polymers is due to the unpredictability in miscibility and phase behavior of the polymers. However, blended polymers continue to be examined across various industries for their application in drug delivery, membrane separation or filtration, battery electrolytes, etc.

Research states that ideal solid-state electrolytes will have the ionic conductivity of a liquid, mechanical properties of a solid and convertibility into thin film structures with large surface area (Jeddi et al.) [6]. Poly (ethylene oxide) at high molecular weights has been widely examined for solid-state electrolytes because it has the ability to dissolve high concentrations of various metal salts (Gurusiddappa et al.) [5]. Although, PEO polymer chains have a high crystallinity which reduces ionic conductivity of the polymer matrix. This has become a major challenge when fabricating PEO-based solid-state electrolytes (Xue et al.) [13]. Accordingly, blending of the PEO with another polymer is one method being utilized to reduce the crystallization PEO. Poly acrylates are commonly used as co-monomers to increase plasticity of rigid polymers (McGraw-Hill) [10]. Poly methacrylates, such as poly (methyl methacrylate) (PMMA) or poly (butyl methacrylate) (PBMA), contain double bonds that are very reactive in polymer processing. Studies have shown that poly (methyl methacrylate) and poly (ethylene oxide) are miscible for various compositions and molecular weights (Marco et al) [8]. This specific polymer blend has also been examined for enhanced ionic conductivity and nano-confinment and research determined that the product had high mechanical strength but ionic conductivities much lower than conventional polymer electrolytes (Jeddi et al.) [6]. Thus the question arose, how do other poly acrylates compare to these results?

The project goal is to determine the miscibility between poly (ethylene oxide) (PEO) and poly (butyl methacrylate) at similar weight fractions and varying compositions. The following will identify key concepts absorbed from literature reviews, the experimental procedure executed, the progress of the project, future plans for the project and conclusions.

2. LITERATURE REVIEW

Prior to the execution of the project, extensive literature review was completed to obtain more knowledge about the topic. The following sections include phase diagrams and behavior, Flory-Huggins regular solution model, and instrumentation utilized for analysis. These sections further explain concepts discovered in reference studies that are significant information to understand in this research project.

i. Phase Diagrams and Behavior

When investigating the miscibility and phase behavior of polymer blends, it is important to understand the phases of polymers and how to generate phase diagrams. All phases are displayed below in Figure 1. The figure represents a plot of composition versus temperature.

Figure 1. Phase Diagram [image found on google search].

Polymers can either exhibit a lower critical solution temperature (LCST), meaning it undergoes a phase separation when heated, or an upper critical solution temperature (UCST) where it undergoes the phase separation upon cooling. The area between the two curves indicate a single-phase or miscible region. The outermost curve is called the bimodal curve which represents the initiation of phase separation or un-mixing. The phase separation takes place when a single-phase system suffers a change of either composition, temperature or pressure (Anderson, Bistra) [2]. The meta-stable regions represent the state of apparent equilibrium that is capable of changing to a more stable state (Anderson, Bistra) [2]. Transitioning from the single-phase to the meta-stable region indicates slow nucleation followed by growth of phase domains, resembling crystallization (Anderson, Bistra) [2]. The spinodal curve represents another point of un-mixing until finally, the phase separated region is achieved. Transitions from the single-phase to the spinodal region happen via spinodal decomposition (Anderson, Bistra) [2].

The phase behavior can also be determined thermodynamically:

By definition, the complete miscibility of the mixture is:

Where is the Gibbs free energy of mixing, is the enthalpy of mixing, is the entropy of mixing, and T is the temperature (Anderson, Bistra) [2].

The entropic term ( remains positive due to the increase in entropy upon mixing therefore, to be miscible the enthalpic term must be less than the entropic term.

In terms of binary composition at fixed temperatures and pressures the criteria becomes:

For phase separation at the spinodal curve:

ii. Flory-Huggins Regular Solution Model

The thermodynamics of binary polymer solutions were first investigated by Paul Flory and Maurice Huggins in the early 1940s. Their work lead to the development of a mathematical model known as the Flory-Huggins regular solution model and is defined below:

The Gibbs free energy of mixing is dependent on the number of moles, n1 and n2, the volume fractions, and , and the polymer-solvent interaction parameter, also known as the Flory-Huggins interaction parameter (Ruzette et al.) [11].

The model makes three major assumptions:

1. It is incompressible and exhibits no volume change during mixing

2. The entropy of mixing is only dependent on the combinatorial entropy

3. The enthalpy of mixing is caused by interactions of different segments after the dissolution of interactions of the same type of segments.

The Flory-Huggins interaction parameter is used to describe the heat of mixing and is defined as:

Where represents the excess exchange interaction energy, z is the lattice coordination, is the nearest-neighbor van der Waals interaction energy between segments i and j and k is the Boltzmann constant (Ruzette et al.) [11].

iii. Instrumentation for Analysis

Literature review assisted in the selection of the proper instrumentation for this project. Furthermore, investigation was performed to understand the operation of each tool. The instruments discussed in this section can determine the miscibility of polymer blends.

Cloud Point Analyzers utilize built in cooling systems and optics to detect the temperature at which a phase separation initially occurs; defined as the cloud point [1]. They are commonly used in the petroleum industry. They utilize several analysis techniques determined by the Analytical Society for Testing Materials (ASTM) such as ASTM D2500, D7346, etc. They are convenient because they can include automated samplers to test multiple samples automatically. Below are two figures that display types of cloud point analyzers.

Figure 2. CPP 5G from A Roper Company [1].

Differential Scanning Calorimetry (DSC) is a technique used to study the thermal transitions of polymers between phases. A thermogram is generated, which plots the heat flow as a function of temperature. A DSC contains two pans, one contains the polymer blend and the other remains the reference. The heat rate is set and remains constant as it is applied to each pan simultaneously. The difference in heat outputs between the reference (empty) pan and the pan with polymer are plotted on the thermogram. Phase changes can be recognized by the peaks on a thermogram as shown in Figures 4 and 5 below. [3]

Figure 3. DSC Operation [3].Figure 4. CrystallizationFigure 5. Glass

peak on a thermogram [3].transition on a thermogram [3].

Figure 6. DSC used for analysis in Genesis B, Room 104.

3. EXPERIMENT

i. Solution Casting

1. Prepare polymer blends

a. Polymers utilized are displayed below in Table I.

Table I. Experimental Polymers

Material

Mw (g/mol)

Monomer M0 (g/mol)

Weight Fraction

(

Glass Transition Temperature (Tg) (C)

Poly (butyl methacrylate)

337000

142.2

2369.90

20

Poly (ethyl methacrylate)

340000

114.14

2978.80

65

Poly (methyl methacrylate)

120000

100.121

1198.55

105

Poly (ethylene oxide)

100000

44.05

2270.15

-66

Data retrieved from Sigma Aldrich [12].

b. A total of 500mg were prepared for each blend.

c. Weigh out each polymer sample for the varying weight compositions from 100 wt% PBMA to 10 wt%, in increments of 10 wt% (i.e. 100wt%, 90wt%, etc.).

2. Add 5 mL of toluene to polymer blends while continuing to stir until completely polymers are completely dissolved.

Figure 7. Mixed polymer blend in Toluene.

3. Cast 1 mL samples of polymer/toluene blends onto a glass dish/slide.

Figure 8. Experimental Set-up and casted samples.

4. Let casted samples sit under fume hood to evaporate toluene at room temperature for 1 to 7 days.

5. Evaporate excess solvent by placing casted samples in a vacuum oven for 2 to 4 days at 45C.

6. Perform full vacuum set at 70C for 24 hours.

7. Analyze results.

ii. Analysis

The phase behavior was analyzed both under a microscope and using a DSC instrument.

Prepare samples for DSC:

1. Weigh Tzero pan with lid and record.

a. Tzero pan: T 160202

b. Tzero lid: T 151126

2. Weigh out a polymer sample size between 5-10mg.

3. Fit polymer sample into pan, replace lid, and press closed.

Figure 9. Pressed DSC pan

4. Adjust DSC run mechanism.

a. Heat/cool/heat method

b. Ramp 5C/min to -80C

c. Ramp 10C/min to 80C

5. Save new run for each sample.

6. Analyze thermogram.

4. PROGRESS AND FUTURE PLANS

i. Progress

The work accomplished this semester lead to the development and approval of an experimental safety plan (ESP). The ESP includes the solution casting procedure and analysis using a microscope, DSC and micro-rheology. Materials were ordered and ten samples were prepared for blends of poly (ethylene oxide) and poly (butyl methacrylate) for various weight compositions. Few results were generated from analysis under a microscope and DSC and are discussed in the following section.

ii. Results

The ten prepared, casted samples can be seen in Figure 8. The image was taken after three days of evaporation at room temperature. A white crystalline powder appeared in several of the samples with increasing PEO weight compositions (PEO > 90 wt%). Of the ten blended samples prepared, three were analyzed under a microscope. The following figure displays the results:

PBMA60/PEO40, 100XPBMA70/PEO30, 100XPBMA80/PEO20, 100X

Figure 10. Microscope images of PBMA/PEO blends.

Figure 10 above represents PBMA/PEO blends of three different samples: PBMA at 60 wt%/PEO at 40 wt%, PBMA at 70 wt%/PEO at 30 wt%, and PBMA at 80 wt%/PEO at 20 wt%, respectively. No heat or cooling was applied to the slide during analysis. Crystals can be seen in each sample above, however the greatest crystallization appears in the PBMA60/PEO40 blend.

Following the visualization under a microscope, samples with PBMA weight compositions of 60 or greater were analyzed using DSC. The thermogram results are displayed below in Figures 11 through 15. Estimated glass transition temperatures from the DSC results are displayed in Table II.

Figure 11. DSC of PBMA at 100 wt%.

Figure 12. DSC of PBMA at 90 wt%, PEO at 10 wt%.

Figure 13. DSC of PBMA at 80 wt%, PEO at 20 wt%.

Figure 14. DSC of PBMA at 70 wt%, PEO at 30 wt%.

Figure 15. DSC of PBMA at 60 wt%, PEO at 40%.

Table II. Estimated Tg and Tm from thermograms

PBMA Composition (wt %)

Glass Transition Temperature (Tg) (C)

Melting Temperature (Tm) (C)

100%

20

-

90%

20

65

80%

27

61

70%

30

66

60%

30

68

iii. Future Plans

Much was achieved in the duration of this project, but future research can be done. For instance, research would include the completion of poly (ethyl methacrylate)/poly (ethylene oxide) sample blends for comparison. The addition of ionic liquids such as Lithium Perchlorate would also be investigated to identify ionic conductivity in comparison to PEO/PMMA blends. Along with the investigation of new materials, it would also be interesting to implement the use of theoretical models to predict phase behavior during analysis.

5. CONCLUSIONS

In conclusion, the thermograms display one glass transition and one melting temperature, insinuating that the polymer blend is miscible. However, the melting temperature appears to be very similar to the melting temperature of poly (ethylene oxide) (Tm= 66C). Consequently, it is too difficult to determine by DSC if miscibility occurred. Similarly, the results achieved via microscope cannot be used to determine miscibility either. This is because, the polymers could not be visualized at a magnification greater than 100X and no heating or cooling was applied to help visualize phase transitions. Therefore, without the analysis by a third instrument such as FTIR or NMR, the results appear inconclusive.

There were many opportunities for error while executing this experiment that could have occurred leading to inconclusive results. First of all, there was a lack of experience performing the solution casting procedure. The polymer solution may have been casted earlier than it should have been leading to an immiscible polymer. Secondly, the vacuum step of the procedure was not completed. Thirdly, there was inexperience running the DSC. Meaning, the method of the DSC may have not been adequate.

Ultimately, the purpose of this research project was to determine the miscibility of poly (ethylene oxide) and poly (butyl methacrylate) at varying weight compositions. The results discovered were inconclusive and the goal was not achieved. Future work should include a second attempt at this procedure to verify results.

REFERENCES

[1] Analytical Instruments for Lab and Process Applications. PAC L.P. A Roper Company, n.d. Web. 27 Sept. 2016.

[2] Andersen, Bistra. Investigations on Environmental Stress Cracking Resistance of LDPE/EVA Blends. Diss. Halle (Saale), U, Diss, 2004. PDF.

[3] "Differential Scanning Calorimetry." Polymer Science Learning Center, 2016. Web. 27 Sept. 2016.

[4] "Flory-Huggins Lattice Theory of Polymer Solutions, Part 1." Polymer Properties Database. Polymerdatabase.com, 2015. Web. 28 Sept. 2016.

[5] Gurusiddapppa, J., W. Madhuri, R. Padma Suvarna, and K. Priya Dasan. "Electrical Properties of PEO-Based Electrolytes." International Journal of Innovative Research in Science, Engineering and Technology November 2015 4.11 (2015): 11447-1454. Ijirset.com. Web. 28 Nov. 2016.

[6] Jeddi, Kazem, Nader Taheri Qazvini, Seyed Hassan Jafari, and Hossein Ali Khonakdar. Enhanced Ionic Conductivity in PEO/PMMA Glassy Miscible Blends: Role of Nano-Confinement of Minority Component Chains. Journal of Polymer Science: Part B Polymer Physics. 48, 2065-2071.

[7] Kuo, Shiao Wei, and Feng Chih Chang. "Miscibility and Hydrogen Bonding in Blends of Poly (vinylphenol-co-methyl Methacrylate) with Poly (ethylene Oxide)." Macromolecules 34 (2001): 4089-097. American Chemical Society.

[8] Marco, C., J.G. Fatou, M.A. Gomez, Hajime Tanaka, and A.E. Tonelli. "Molecular Weight Effect on the Miscibility of Poly (ethylene Oxide) and Isotactic Poly (methyl Methacrylate) in Their Blends." Macromolecules 23 (1990): 2183-188. American Chemical Society.

[9] Paul C. Painter and Michael M. Coleman. Essentials of Polymer Science and Engineering. Destech Publications, Inc. 2009.

[10] "Polyacrylate." McGraw-Hill Dictionary of Scientific & Technical Terms, 6E. 2003. The McGraw-Hill Companies, Inc. 21 Sept. 2016.

[11] Ruzette, Anne-Valerie G., and Anne M. Mayes. "A Simple Free Energy Model for Weakly Interacting Polymer Blends." Macromolecules 34 (2001): 1894-907. American Chemical Society.

[12] Sigma-Aldrich. Sigma-Aldrich Co. LLC., n.d. Web. 27 Sept. 2016.

[13] Xue, Zhigang, Dan He, and Xiaolin Xie. "Poly (ethylene Oxide)-based Electrolytes for Lithium-ion Batteries." Journal of Materials Chemistry A 3.38 (2015): 19218-9253. Web. 28 Nov. 2016.